fsmFsPath() no longer needs the fsm, file iterator is enough
Pass mode as argument into fsmBackup()

- No functional change, just reducing the places depending on fsm->[o]sb
Eliminate couple of unnecessary more fsm->sb uses

- Use rpmfiFMode() directly, that's where the data really comes
  from in these cases
Pass stat buffers as arguments to fsmVerify()
Pass stat buffers as arguments to fsmInit()
Minimally eliminate sb and osb members from fsm struct

- Doesn't seem to make a whole lot of sense in itself, but a required
  intermediate step to make sense of this whole mess
Get rid of the pointer "shortcuts" to sb & osb structs
Sanitize the fsm stat buffer business a bit

- Only install needs two stat structs: one for the to-be-installed
  package which is populated from rpmfi data, and the other which
  reflects on-disk data in case where replacing something. Remove
  only cares about on-disk state, so we dont need two.
- This is not supposed to change anything, famous last...
Inline fsmReset() into fsmInit(), having these separate makes no sense
Eliminate pointless mapFlags member from fsm

- These days there's nothing but CPIO_SBIT_CHECK which we might just
  as well do always: there's not a whole lot benefit doing the check
  for src.rpm installs but its not exactly harmful either.
Eliminate pointless diskchecked member from fsm too

- Disk is always checked, unless fsmMapPath() fails ... which cannot
  happen, and would not make a difference here either way.
Use symlink data from header, not payload

- Besides avoiding ugly "lets pass arguments through this handy
  looking unrelated struct member" behavior, verify the contents
  as well: symlinks dont have digests but we can strcmp() them
  easily enough to achieve the same.
Get rid of no longer needed fsm->buf[size]